Interpretive Summary: Understanding the impact of climate change on future global crop production is critical for the assessment of potential adaptation strategies. There are numerous crop models for the prediction of maize growth and yield; however, these models have not been evaluated against common data sets and this project was designed to evaluate the available 23 maize models. The inter-comparisons were conducted by a team of international investigators using observed weather and maize growth and yield data from four locations around the world. Individual models varied in their ability to predict yields; however, the ensemble of models predicted the absolute yields with a great deal of certainty. An evaluation of temperature effects showed a greater impact on maize yield than increasing carbon dioxide with an estimate of a decrease in grain yield of 8 bushels per acre for each 1.5 F temperature increase. To estimate the impact of future climate on maize production requires improved simulation models capable of incorporating the effects of a changing climate and these results suggest an ensemble of models may be required to achieve this goal. This information is of value for the agronomic and climate research community and policymakers dealing with climate assessments and future crop production.

Technical Abstract:
Potential consequences of climate change on crop production can be studied using mechanistic crop simulation models. While a broad variety of maize simulation models exist, it is not known whether different models give similar grain yield responses to changes in climatic factors, or whether they agree in their general trends related to phenology, growth and yield. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations [CO2], we present the largest maize crop model inter-comparison to date, including 23 different models. These models were evaluated for four locations representing a wide range of maize production conditions in the world: Lusignan (France), Ames (USA), Rio Verde (Brazil) and Morogoro (Tanzania). Temperature increase had a much larger influence on modeled yield response than did increased [CO2] and caused overall decrease of yield of roughly 0.5 Mg per °C. Doubling [CO2] from 360 to 720 µmol mol-1 increased grain yield by 7.5% on average across models and the sites. There was a large uncertainty in the response to [CO2] among models. Model responses to temperature and [CO2] factors did not differ whether models were simulated with low calibration information or simulated with high level of calibration information. While individual models differed considerably in absolute yield simulation at the four sites, the ensemble of the models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that using an ensemble of models has merit. The ensemble response to temperature and [CO2] was not dependent on the level of calibration information.